The present invention relates to an offset printing machine, and more particularly, to sheet transfer from a sheet feed cylinder to an impression cylinder and from the impression cylinder to a sheet discharge portion.
Multiple color offset printing machines are known for printing in multiple colors. For example, Japanese Patent Application Publication Toku-Hyou-Hei-9-510410 discloses a four color offset printing machine in which a single impression cylinder, a single sheet discharge mechanism, a single sheet feed conveyor (feeder), a single sheet feed cylinder (sheet transfer cylinder), two blanket cylinders, two plate cylinders, and ink roller groups for four colors are provided.
A sheet feed mechanism including the sheet feed conveyor and the sheet feed cylinder is adapted for supplying a sheet to a surface of the impression cylinder. The impression cylinder has an outer peripheral surface where the sheet is held. The sheet discharge mechanism is adapted to remove the sheet from the surface of the impression cylinder. The blanket cylinders are adapted to press the sheet against the impression cylinder to form an ink image on the sheet.
The outer peripheral surface of the impression cylinder is provided with grippers, each gripper having a pawl at its tip for holding a sheet. The impression cylinder is equally divided into three segments for holding each sheet at each segment, and is driven by a drive motor. Axes of the blanket cylinders and the paper feed cylinder are disposed in parallel with the axis of the impression cylinder, and outer peripheral surfaces of the blanket cylinders and the paper feed cylinder are in contact with the outer peripheral surface of the impression cylinder. The blanket cylinders, the sheet feed conveyer, the sheet feed cylinder, and the sheet discharge mechanism are driven by rotation of the impression cylinder.
Each plate cylinder is formed with a plate at its outer peripheral surface. The axes of the two plate cylinders are disposed in parallel with the axes of the two blanket cylinders, and each plate cylinder is in contact with a corresponding blanket cylinder, so that each plate cylinder is rotated by the rotation of the corresponding blanket cylinder. The outer peripheral surface of each plate cylinder is equally divided into two plate segments, and each plate segment has a peripheral length equal to that of each segment of the impression cylinder. Each plate segment is formed with a plate for one specific color, and a different color is associated with each plate. Therefore, a total of four plates for four different colors are formed in the two plate cylinders.
Each ink roller group is adapted for supplying ink to the plate on the plate cylinder. Two groups of ink rollers are provided for one plate cylinder so as to supply inks of two colors. Therefore, four groups of ink rollers are provided for supplying inks of four different colors. The ink rollers have axes in parallel with the axis of the plate cylinder, and are in contact with the plate cylinder. The ink rollers are rotated by the rotation of the plate cylinder.
In this way, in the offset printing machine capable of performing four color printing with the two blanket cylinders, each sheet is printed with two colors during each single rotation of the impression cylinder, and printing of the additional two colors is performed during the second rotation of the impression cylinder. That is, each sheet is held on the impression cylinder for two rotations thereof, and thereafter must be released from the impression cylinder by the sheet discharge mechanism. If each sheet is supplied to the impression cylinder at every single rotation of the impression cylinder, it becomes impossible to perform four color printing with respect to each sheet. To avoid this, a sheet is supplied to every other segment of the impression cylinder. For example, if a sheet is supplied to a first segment, then, a sheet is not supplied to a second segment, but a sheet is supplied to a third segment. The supplied sheet is held on the impression cylinder until completion of two rotations thereof and is then discharged from the impression cylinder by the sheet discharge mechanism.
No specific arrangement is proposed in the Japanese patent application publication No.Toku-Hyou-Hei 9-510410 for supplying a sheet to every other segment of the impression cylinder.
One conceivable arrangement is to design the outer peripheral length of the sheet feed cylinder equal to the peripheral length of each segment of the impression cylinder, and supply a sheet to the impression cylinder at every twice rotation of the sheet feed cylinder. However, when a sheet is transferred from the sheet feed cylinder to the impression cylinder, each time one of the impression cylinder pawls holding a sheet at an outer periphery of the impression cylinder intersects with sheet feed cylinder pawls for holding a sheet to the outer periphery of the sheet feed cylinder, a sheet cannot be maintained at the outer periphery of the impression cylinder for more than a single rotation of the impression cylinder.
Further, each of the impression cylinder pawls protrudes radially outwardly from the outer peripheral surface of the impression cylinder, and the sheet feed cylinder pawls protrude radially outwardly from the outer peripheral surface of the sheet feed cylinder. Also, recesses are formed in the section of the impression cylinder and the sheet feed cylinder that confronts the protruding pawls. Therefore, when the pawls of the sheet feed cylinder and the impression cylinder intersect without transferring a sheet, that is, for maintaining a sheet on the peripheral surface of the impression cylinder, the pawl provided to the sheet feed cylinder and protruding toward the corresponding recess on the impression cylinder pushes the sheet held on the impression cylinder, and possibly tears the sheet.
It is an object of the present invention to provide an offset printing machine capable of maintaining a sheet held on the impression cylinder without damaging the sheet by the pawl on the sheet feed cylinder when the pawl on the sheet feed cylinder relatively passes through the pawls on the impression cylinder and when there is no need to transfer a sheet from the sheet feed cylinder to the impression cylinder.
This and other objects of the present invention will be attained by an offset printing machine for forming an image on a sheet including a plate cylinder, a blanket cylinder, an impression cylinder, impression cylinder grippers, a sheet feed cylinder, a sheet feed cylinder gripper, an improved sheet feed side impression cylinder gripper drive mechanism, and an improved sheet feed cylinder gripper drive mechanism. The plate cylinder is rotatable about its axis and has an outer peripheral surface equally divided in a circumferential direction into at least two color regions. An ink image is formed on each color region and each color region has an equal circumferential length. The blanket cylinder is rotatable about its axis and has an outer peripheral surface in contact with the color regions and is equally divided in a circumferential direction into at least two color sections. Each ink image on each color region is transferred to each color section, and each color section has an equal circumferential length. The impression cylinder is rotatable about its axis and has an outer peripheral surface on which the sheet is held and transferred. Each color section is in contact with the outer peripheral surface of the impression cylinder for transferring each ink image on each color section onto the sheet. The outer peripheral surface of the impression cylinder is equally divided into a plurality of segments each having a peripheral length equal to the circumferential length of the color region and the color section. The impression cylinders are provided at the outer peripheral surface of the impression cylinder and are movable along with the rotation of the impression cylinder. Each impression cylinder gripper is positioned at each leading end portion of each segment, and each impression cylinder gripper is movable between an open position and a closed position. The sheet feed cylinder is rotatable about its axis and has an outer peripheral surface on which a sheet is held and transferred and in contact with the outer peripheral surface of the impression cylinder at a contact position for transferring the sheet to the impression cylinder. The outer peripheral surface of the sheet feed cylinder has a peripheral length equal to a peripheral length of each of the segments. The sheet feed cylinder gripper is provided at the outer peripheral surface of the sheet feed cylinder and is movable along with the rotation of the sheet feed cylinder. The sheet feed cylinder gripper and the impression cylinder gripper is so positioned to simultaneously reach the contact position. The sheet feed cylinder gripper is movable between an open position and a closed position. The sheet feed side impression cylinder gripper drive mechanism is adapted for moving the impression cylinder gripper to either its open position or closed position at the contact position. The sheet feed cylinder gripper drive mechanism is adapted for moving the sheet feed cylinder gripper to either its open position or closed position. A combination of the sheet feed side impression cylinder gripper drive mechanism and the sheet feed cylinder gripper drive mechanism includes means for providing a sheet transfer timing by switching the impression cylinder gripper from its open position to its closed position and by switching the sheet feed cylinder gripper from its closed position to its open position at a predetermined timing of confrontation between the impression cylinder gripper and the sheet feed cylinder gripper at the contact position. The predetermined confronting timing occurs when the confronting times is equal to the number of the color sections of the blanket cylinder. The sheet feed side impression cylinder gripper drive mechanism includes means for maintaining the closed position of the impression cylinder gripper when the impression cylinder gripper passes by the contact position but except the predetermined confronting timing. The sheet feed cylinder gripper drive mechanism includes means for maintaining the open position of the sheet feed cylinder gripper when the sheet feed cylinder gripper passes by the contact portion but except the predetermined confronting timing. A combination of the maintaining means of the sheet feed side impression cylinder gripper drive mechanism and the maintaining means of the sheet feed cylinder gripper drive mechanism constituting the providing means.
In another aspect of the invention, there is provided an offset printing machine for forming an image on a sheet including a frame, the plate cylinder, the blanket cylinder, the impression cylinder those supported on the frame, the impression cylinder gripper, the sheet feed cylinder, the sheet feed cylinder gripper, an improved sheet feed side impression cylinder gripper drive mechanism, and an improved sheet feed cylinder gripper drive mechanism. The sheet feed side impression cylinder gripper drive mechanism is adapted for moving the impression cylinder gripper to either its open position or closed position at the contact position. The sheet feed cylinder gripper drive mechanism is adapted for moving the sheet feed cylinder gripper to either its open position or closed position. The sheet feed side impression cylinder gripper drive mechanism includes a cam shaft, a first cam, a first grip switching cam, and a first link mechanism. The cam shaft is rotatably supported by the frame, and is rotated once each time the impression cylinder rotates a predetermined number which is the number of the color sections divided by the number of the segments. The first cam is provided integrally with the cam shaft and is rotatable together with the cam shaft. The first cam has a front half first cam surface area and a rear half second cam surface area. The first grip switching cam is supported to the frame and is movable between an abutment position and a non-abuttable position. In the abutment position, the first grip switching cam is abuttable on the impression cylinder gripper for moving the impression cylinder gripper from their closed position to their open position and then to the closed position when each one of the impression cylinder grippers passes by the contact position. In the non-abutment position, the grip switching cam is positioned spaced away from the impression cylinder grippers for maintaining the impression cylinder grippers to their closed position. The first link mechanism has one end in contact with the first cam and movable in accordance with a contour of the first cam, and has another end connected to the first grip switching cam for moving the first grip switching cam between the abutment position and the non-abutment position. The abutment position is provided by the contact of the one end with the first cam surface area, and the non-abutment position is provided by the contact of the one end with the second cam surface area. The sheet feed cylinder gripper drive mechanism includes a second cam, a second grip switching cam, a fixed cam, and a second link mechanism. The second cam is provided integrally with the cam shaft and is rotatable together with the cam shaft. The second cam has a front half cam surface area and a rear half cam surface area. The front half cam surface area is superposed with the second cam surface area of the first cam and the rear half cam surface area is superposed with the first cam surface area of the first cam. The second grip switching cam is supported to the frame and is movable between an abutment position abuttable on the sheet feed cylinder gripper for moving the sheet feed cylinder gripper from its closed position to its open position when the sheet feed cylinder gripper passes by the contact position and non-abutment position spaced away from the sheet feed cylinder gripper for maintaining the sheet feed cylinder gripper to its closed position. The fixed cam is fixed to the frame and is positioned downstream of the second grip switching cam with respect to a rotational direction of the sheet feed cylinder. The sheet feed cylinder gripper is abutable on the fixed cam for providing open position of the sheet feed cylinder gripper. The second link mechanism has one end in contact with the second cam and movable in accordance with a contour of the second cam, and has another end connected to the second grip switching cam for moving the second grip switching cam between the abutment position and the non-abutment position. The abutment position is provided by the contact of the one end with the rear half cam surface area, and the non-abutment position is provided by the contact of the one end with the front half cam surface area.
In still another aspect of the invention, there is provided an offset printing machine for forming an image on a sheet including the plate cylinder, the blanket cylinder, the impression cylinder, the impression cylinder grippers, a sheet discharge mechanism, an improved sheet discharge side impression cylinder gripper drive mechanism, and an improved sheet discharge gripper driving mechanism. The sheet discharge mechanism includes two sprockets, an endless chain, and at least two sheet discharge grippers. The two sprockets are rotatable about their axes extending in a direction parallel with the axis of the impression cylinder. The endless chain is mounted on the sprockets and is movable by the rotation of the sprockets. The at least two sheet discharge grippers are fixed to the endless chain and is equidistantly spaced away from each other. Each of the discharge grippers are movable between its open position for receiving and releasing a sheet and closed position for holding a sheet. The impression cylinder grippers and the discharge grippers provide a positional relationship that any one of the impression cylinder grippers reaches a discharge position between the impression cylinder and the sheet discharge mechanism when one of the sheet discharge grippers reaches the discharge position. The sheet discharge side impression cylinder gripper drive mechanism is adapted for moving each one of the impression cylinder grippers between its open position and closed position at the sheet discharge position. The sheet discharge gripper driving mechanism is adapted for moving each one of the sheet discharge grippers between its open position and closed position at the sheet discharge position. The sheet discharge side impression cylinder gripper drive mechanism includes means for maintaining the closed position of the impression cylinder gripper when the impression cylinder gripper passes by the sheet discharge position provided that any one of the sheet discharge grippers is positioned offset from the sheet discharge position. At least two sheet discharge grippers and the impression cylinder grippers provide a positional relationship so that one of the impression cylinder grippers is in confrontation with one of the sheet discharge grippers at a predetermined timing occurring at every predetermined number of access of any one of the impression cylinder grippers to the sheet discharge position. The predetermined number is equal to the number of color sections of the blanket cylinder.
In still another aspect of the invention, there is provided an offset printing machine for forming an image on a sheet including a frame, the plate cylinder, the blanket cylinder, the impression cylinder those supported on the frame, the impression cylinder grippers, the sheet discharge mechanism, and an improved sheet discharge side impression cylinder gripper drive mechanism, and an improved sheet discharge gripper driving mechanism. The sheet discharge side impression cylinder gripper drive mechanism is adapted for moving each one of the impression cylinder grippers between its open position and closed position at the sheet discharge position. The sheet discharge gripper driving mechanism is adapted for moving each one of the sheet discharge grippers between its open position and closed position at the sheet discharge position. The at least two sheet discharge grippers and the impression cylinder grippers provide a positional relationship so that one of the impression cylinder grippers is in confrontation with one of the sheet discharge grippers at a predetermined timing occurring at every predetermined number of access of any one of the impression cylinder grippers to the sheet discharge position. The predetermined number is equal to the number of color sections of the blanket cylinder. The sheet discharge side impression cylinder gripper drive mechanism includes a cam shaft, a cam member, a discharge grip switching cam, and a link mechanism. The cam shaft is rotatably supported by the frame, and is rotated once each time the impression cylinder rotates a predetermined number which is the number of the color sections divided by the number of the segments. The cam member is provided integrally with the cam shaft and is rotatable together with the cam shaft. The cam member has a front half first cam surface area and a rear half second cam surface area. The discharge grip switching cam is supported to the frame and is movable between an abutment position abuttable on the impression cylinder grippers for moving the impression cylinder grippers from their closed position to their open position when each one of the impression cylinder grippers passes by the sheet discharge position and non-abutment position spaced away from the impression cylinder grippers for maintaining the impression cylinder grippers to their closed position. The link mechanism has one end in contact with the cam member and movable in accordance with a contour of the cam member, and has another end connected to the discharge grip switching cam for moving the discharge grip switching cam between the abutment position and the non-abutment position. The abutment position is provided by the contact of the one end with the first cam surface area, and the non-abutment position is provided by the contact of the one end with the second cam surface area, whereby the closed position of the impression cylinder gripper is maintained when the impression cylinder gripper passes by the sheet discharge position provided that any one of the sheet discharge gripper is positioned offset from the sheet discharge position.
According to the above described offset printing machine, by the sheet feed side impression cylinder gripper drive mechanism and the sheet feed cylinder gripper drive mechanism, the impression cylinder gripper and the sheet feed cylinder gripper perform sheet transfer operation at a predetermined timing of confrontation between the impression cylinder gripper and the sheet feed cylinder gripper at the contact position. The confronting timing occurs when the confronting number is equal to the number of the color sections of the blanket cylinder. Except the predetermined confrontation timing but when the impression cylinder gripper and the sheet feed cylinder gripper reach the contact position, the impression cylinder gripper is maintained in its closed position as it pass by the contact position and the sheet feed cylinder gripper is maintained in its open position as they pass by the contact position. Accordingly, a sheet is transferred from the sheet feed cylinder to the impression cylinder only once each number of times the blanket cylinder is divided into color regions. When no sheet transfer is performed, the sheet feed cylinder grippers provided on the sheet feed cylinder will not damage the sheet held on the outer peripheral surface of the impression cylinder.
Further, according to the above described offset printing machine, the sheet discharge grippers are separated from each other along the length of the chain by a distance equal to the outer peripheral length of the blanket cylinder, and are positioned to meet with an impression cylinder gripper at the discharge position of a sheet to transfer the sheet from the impression cylinder gripper to the sheet discharge gripper. The sheet discharge is performed at a predetermined timing of confrontation between the impression cylinder gripper and the sheet discharge gripper at the sheet discharge position. The predetermined confrontation timing occurs at every predetermined number of access of the impression cylinder gripper to the discharge position, the predetermined number being equal to the number of color sections of the blanket cylinder. Accordingly, a sheet is transferred from the impression cylinder to the sheet discharge mechanism at the predetermined confrontation timing. When no sheet transfer is being performed, there is no danger that the sheet discharge grippers provided to the sheet discharge mechanism will damage the sheets supported on the outer peripheral surface of the impression cylinder.